Porous materials are classified into microporous materials, mesoporous materials and macroporous materials according to their pore sizes. Although the boundary of the classification is not clear, it is roughly divided into the following; microporous materials with pore sizes ranging less than about 2 nm, mesoporous materials with pore sizes ranging from about 2 to 50 nm, and macroporous materials with pore sizes ranging about more than 50 nm.
Microporous materials include zeolites and pillared clays. Typical mesoporous materials include xerogels such as silica gels and silica alumina gels, and porous glasses synthesized using phase-separation of glasses. Mesoporous materials are widely utilized in chemical industries as adsorvents for separation and purification of materials, catalysts, catalyst supports, supports for enzyme immobilization and so on. Microporous materials have the functions of selective adsorption of molecules based on their pore sizes, which are therefore used mainly for small size molecules, while mesoporous materials have larger pore sizes and have widespread demands over general processes of chemical industries. In these days, the demands for porous materials are concerned not only with the pore sizes, pore size distribution, and surface area, but also with the chemical interaction with adsorbates; the demands include mesoporous materials having weak solid acidity, and porous materials having hydrophobicity. The demands on the materials are diverse and mesoporous materials using new materials are required.
As conventional mesoporous materials, xerogels based on silica or alumina and porous glasses have been mainly used. These porous materials have a feature of strong solid acidity and are used for cracking catalysts and the like; however, its strong solid acidity limits applications. For this reason, hydrophobic mesoporous materials of weak solid acidity and small polarity are eagerly awaited.
On the other hand, while various aluminum phosphate (AlPO4)-based porous materials are known and are receiving attention as hydrophobic adsorbing materials of weak acidity, all the AlPO4-based porous materials known so far are microporous materials. For example, materials with a maximum pore size are AlPO4—H1 or VPI-5, containing oxygen 18-membered rings, the pore sizes of which are only 1 nm. The emergence of AlPO4-based mesoporous materials having a pore size of 2 nm or larger is awaited with hope.
It is an object of the present invention to provide mesoporous materials with hydrophobic, weak solid acidity and small polarity.